Ultrasound technique is generally known for the examination of workpieces or material regions. Ultrasound is thereby beamed into the material by means of a probe and the reflection is detected and evaluated. For the examination of rails by ultrasound, a plurality of probes is used which is placed on the stretch of rails, a coupling medium, normally water, being used for coupling the probes to the rail. The probes beam into the rail at respectively different angles and the corresponding reflections are detected and evaluated.
In the case of a rail testing train used at the moment, testing is implemented with the help of respectively 9 probes for 0°, ±20°, ±35° and 2×±70°. However there is a requirement for improvement with respect to extending the probe functions by means of an additional pair of probes of ±55°. Furthermore, the reduction in the use of coupling medium is considered to be necessary, which however counteracts the cited extended use of probes. Also an acceleration in evaluation is regarded as desirable. The technical testing conversion of these development aims is however restricted when using conventional testing technique because the latter is rigid, i.e. it can be adjusted to different track profiles, i.e. rail height, only by means of mechanical retooling, as is the case for the different national rail networks. An increase in the number of probes used in order to obviate this problem is problematic insofar as, as already mentioned, this would result in a greater requirement for coupling medium, which leads above all to supply problems in the case of long travelling distances of the testing train. Also optimal, i.e. flexible adaptation of the acoustic irradiation angles to the testing conditions would be possible only by means of a drastic increase in the probes which are used, which leads to the same problems.
A technically achievable solution would reside in the use of electronically controlled probes, as are used in phased-array technique. It would make respectively only one probe or transducer necessary per rail stretch and travel direction and enable the programme-controlled adjustment of the required angles. Such a technique which has already been used for many years in non-destructive testing with ultrasound and has proved its worth in particular in resolving complex testing tasks, permits optimal adaptation of the sound field parameters, such as acoustic irradiation angle and depth of focus by an electronic route. By reducing the probes to respectively only one phased array probe per rail and direction, furthermore a significant saving in coupling media would be achieved.
From a technical apparatus point of view, the requirement exists hereby however of undertaking the presently required angle adjustments (e.g. 0°, ±35°, ±55°, ±70°) within the travelling speed of the train (maximum 100 km/h) with the required resolution (3 mm). With a time-sequential angle passage as is normal in phased array technique, this is not possible since this would result in a maximum travelling speed of less than 10 km/h. A high travelling speed is however impermissible because of the necessity for adapting to the cycle times of the rail traffic, above all in heavy traffic routes.